This invention relates to the addition of chemical additives to a water treatment system and particularly relates to dynamic optimization of a water treatment system by microprocessor control of additive addition in response to variations in electro chemical noise (RCN), changes in the linear polarization rate (LPR) and variations in the activity factor (AF).
Corrosion of the metals making up the cooling water circulating system is of primary concern to owners and operators of such equipment. Of particular concern is the corrosion of the heat exchangers.
In industrial cooling systems, water from rivers, lakes, ponds, wells, wastewater treatment plant effluent etc., is employed as the cooling media for heat exchangers. These waters can contain a variety of either dissolved or suspended materials such as mineral salts, metals, organics, silt, mud etc. The cooling water from a heat exchanger is typically passed through a cooling tower, spray pond or evaporative system prior to discharge or reuse. In such systems, cooling is achieved by evaporating a portion of the water passing through the system. Because of the evaporation that takes place during the cooling, both dissolved and suspended solids concentrate.
The concentrating of various anionic ions such as chlorides and sulfates can increase the rate of corrosion of the metals making up the cooling system. This is especially true with the metals making up the heat exchangers that are experiencing higher temperatures due to heat transfer. Other contaminates such as hydrogen sulfide can also increase corrosion rates.
Mineral salts such as calcium and magnesium can induce scaling of the heat exchangers that reduces heat transfer. A scale common to many cooling systems is calcium carbonate. Additionally, scales such as calcium phosphate can also inhibit heat transfer as well as induce under deposit corrosion.
Deposit formation on heat exchangers also impedes heat transfer. For example, corrosion byproducts can form on the metal surface where a corrosion cell has formed. Alternatively, deposits from metal oxides, silt, mud, microbiological activity and process contamination can reduce the efficiency of heat transfer as well as increase corrosion.
Reducing the occurrence of corrosion, scaling, and deposition upon heat exchangers and associated cooling system equipment is essential to the efficient and economical operation of a cooling water system.
Excessive corrosion of the metallic surfaces can cause the premature failure of process equipment, necessitating down time for the replacement or repair of the equipment. Additionally, the buildup of corrosion products on the heat transfer surfaces impedes water flow and reduces heat transfer efficiency thereby limiting production or requiring downtime for cleaning.
To effectively apply inhibitors in dynamic conditions such as those described, the real-time performance of the inhibitor program is required. Undetected periods of high pitting rates and/or deposit formation can severely impede both performance and equipment life.
U.S. Pat. No. 4,648,043 teaches a computerized chemical application system for a water treatment system. A computer control senses the conductivity of a reference water flowing through the chemical introduction header and, based upon the differential conductivity and values relating conductivity to concentration for the water treatment liquid, precise control of the amount of water treatment liquid added is achieved.
U.S. Pat. No. 5,213,694 is directed toward a water treatment control system for treating cooling tower makeup water. The system utilizes a source of vacuum applied to an injector valve to draw chemicals from a holding tank into the make-up water.
The present invention describes an apparatus for the optimized control of various treatment chemicals (corrosion inhibitors and supporting treatments) applied for corrosion and/or deposit inhibition. The apparatus consist of a microprocessor system that controls inhibitor concentrations as a result of processed inputted data. The inputted data includes, but is not limited to, values consistent with the monitoring of Electrochemical Noise and Linear Polarization Rate, heat transfer, concentrations of water treatment chemistry, critical water chemistry parameters, and critical operational characteristics. Although the invention has been described with relation to water treatment processes, it is contemplated that the process can further be utilized for process side applications where electrolytes are present, but may be the solute rather than the solvent, e.g. processes dealing with hydrocarbons where water is only present at a very small percentage of the overall solution.
Accordingly, it is an objective of the instant invention to teach a device and a process for its use which can identify corrosion, particularly pitting corrosion, and institute steps to moderate such pitting conditions, under microprocessor control and in real-time thereby avoiding or substantially eliminating the initial stages of pit formation upon all affected metallic surfaces, particularly heat exchange surfaces.
It is an additional objective of the instant invention to integrate, under microprocessor control, the corrosion identifying process with a process for corrosion inhibition which can quickly suppress the corrosion cell(s) by making real-time adjustments to the inhibitor program.
It is yet an additional objective of the instant invention to teach a process for monitoring corrosion values for both electrochemical noise (ECN) and linear polarization rate (LPR) under heat transfer.
It is still an additional objective of the instant invention to teach a method of operation wherein the ECN and LPR values are processed to compare how the corrosion signals correlate.